The present invention relates to a method of controlling the quantity of laser beam light emitted by a semiconductor scanning apparatus of the type used for a writing-in head in a laser beam printer, a digital copy machine and the like, and more particularly, the invention relates to a method of controlling the quantity of light in an electrophotographic apparatus employing a tri-level developing method in which normal and reverse latent images are formed, preferably by a single exposure, and in which two-color development is performed.
A conventional laser printer typically uses one laser scanning light beam and one-color toner for development. However, in recent years, a tri-level developing method has attracted attention as being applicable for use in a laser printer for color printing. For example, such a tri-level developing method is disclosed in U.S. Pat. No. 4,847,655. The tri-level developing method is a method in which one laser scanning light beam forms a normal developed latent image, a reverse developed latent image and an intermediate voltage latent image, which is not performed with either of the other developments, and then a development using toners of two colors is performed at one time.
In an electrophotographic process, when an electrostatic latent image is formed on a photosensitive body, an electric field having a polarity opposite to the polarity of the latent image is formed in a peripheral portion of the latent image, together with an electric field enhancing development formed at the edge portion of the latent image.
The reverse electric field is not a problem in the forming of an image in a conventional one-color development process. However, in the tri-level process in which positive and negative latent images are formed on a photosensitive body and then are developed using toners of two colors (for example, red and black) charged respectively to polarities opposite to the polarities of the latent images, there has been a problem of degraded quality of the two-color picture by appearance of a special phenomenon (hereinafter referred to as a "fringe phenomenon") in which red toner is attached around a black image and black toner is attached around a red image by attraction of the reverse electric field.